Method of testing coated paper



ERADNER ET AL 9 L METHOD OF TESTING COATED PAPER Filed Jan. as, 1923Fetenied Aug,

assists.

munch or resume oosrnp rerun Donald B. Bradncr and William J.Montgomery, Hamilton; Ohio, ossignors to The Champion Paper and FibreCompany, Hamilton, @hio, a

corporation oi @liio Application January 28, 1928, Serial No. 250,252

2d aniline.

This invention relates to an improved method of testing the coatings oncoated paper.

Coated paper is commonly manufactured by applying to paper raw stock a.coating consisting '5 of mineral pigment and en adhesive substance. Themineral pigment may be clay, satin white, blanc fixe, or the like, endthe adhesive substance may be casein, starch, glue, or the like.

In the manufacture of coated paper it is highly l desirable to controlclosely the 'size" of the coating. Size is a function of the adhesionexisting between the coating and the raw stock and the cohesion of thecoating for itseli. A soft sized coated paper is one in which theadhesion existing between the coating and the raw stock and/or thecohesion of the coating for itself is relatively weak. Conversely acoated paper which is hard sized" is one in which the adhesion existingbetween the costing and the raw. stock and/or the cohesion of thecoating i'or itself is relatively strong. If a coated paper is too-"soft sized." the coating will pick on a printing press or the coatingwill flour off. A coated paper which is too "hard sized? does not printas well and does paper, and in addition there is an unnecessaryconsumption of adhesive substance in the produc-' tion of such coatedpaper.

Due to the large number of variables in the manufacture oi coated paperit is practically impossible to consistently obtain the optimum degreeof sizing without a reliable method of testing and controlling the sizeof the coated sheet. For example, the casein, starch, glue or similaradhesive substances are complex chemical bodies which vary somewhat inadhesive properties from lot to lot. Furthermore the quantity 0!adhesive substance required to satisfactorily bind a pigment to thepaper varies with the chemical composition and physical state ofaggregation of the pigment. Thus, for example, two lots of clayfrequently require different quantities of adhesive substance to givecoatings of the same adhesive strength.-

Heretofore, no satisfactory-qualitative or quantitative methods fortesting the writings on coated paper have been-devised. It is true thatseveral tests have been proposed and some are in operation in theindustry. The most common of these 50 tests is what is known as thethumb test. This test consists in moistening the thumb, pressing it uponthe coated paper, removing the thumb and examining it for the quantityof coating'adhering to it. If a considerable quantity of coating adheresto the thumb, the paper is said to be soft not finish "high" as readilyas a correctly coated sized; while it little or no coating adheres tothe thumb, the paper is said to be hard sized. Although widely used,this test is obviously open to a large number of objections due, forexample,

to variations in the amount of moisture on the .5; thumb, the pressureapplied, duration of pressing, the size 0! the thumb, the speed ofremoval from the paper, etc. Furthermore, the test tends to show awsterproof coating harder than it really is, and a non-waterproofcoating softer than 1.0 it really is. It is therefore a commonoccurrencethat two individuals well skilled in the performonce oi thistest fail to agree, and even the same individual does not get consistentresults.

Another test which has been proposed consists 5 in softening a stick ofsealing wax by heat, presshas this upon the coated paper andthen pullingit vertically from the paper. The end of the stick of sealing wax whichhas been in contact with the coated paper is then examined. If the waxhas 0 pulled stock, the paper is supposed to be hard sized; if it pullsconsiderable coating, it is supposed to be soft sized. Although thesetwo tests are the most commonly employed in the industry, neither ofthem is sensitive or reliable.

The object of this invention is to provide an accurate, reliable, andquick qualitative and quantitative method of testing the coatings oncoated paper. l

The method consists in contacting over a considerable area of the coatedpaper a. testing agent consisting of a. thin flexible body having arelatively strong adhesive surface and then suddenly removing it by atsharp pull or jerk with the hand or by mechanical meansin such e. mannerthat the testing agent parts with the coated paper substantially from alinecontact as distinguished from an area contact. The testing agentpulls with it more or less coating or coating and paper stock and byexamination of the adhesive surface of the testing agent a goodqualitative estimate of the adhesion existing between the coating andthe paper stock and the cohesion of the coating for itself is obtained.By using mechanical means which is capable of measuring the force orwork required to remove the testing agent from the paper, a goodquantitative as well as qualitative estimate of the size of the coatingmay be obtained. Thus with a given raw stock the presence of .aconsiderable amount of coating on the testing agent indicates a. softersized coating than does the presence of only a small amount of coating.With a given raw stock the quantity of coating removed is a measure ofthe sizing of the coating. The testing agent may be a flexible bodyconsisting of a relatively strong adhesive substance alone or it mayconsist of a backing composed of cloth, leather, thin metal or any othermaterial of evenly coated or rmpregna wit iemtively strong adhesivesubstance. The adhesive substance may be any desired material providedit does not appreciably soften, dissolve or otherwise adversely affectthe mgredients of the coating composition. Testing agents impregnated orcoated with cured or cured rubber are particularly suitable. The shapeform of the testing agent is immaterial. although we to u relativelynarrow, elongated strip like a rihbon or tape.

For example, one convenient testing agent for carrying out thisinvention is ordinary friction tape and the invention will beparticularly described in connection therewith. For example, a strip offriction tape about eight to ten inches long and about three quarters ofan inch wide is laid firmly and evenly upon the coated paper to betested. A small seam roller is then pressed back and forth over the tapeuntil it thoroughly adheres to the coated paper except at one end, wherea portion large enough to be firmly grasped between the fingers is leftextending out of contact with the paper. The paper is held firmly on asmooth surface with the hand or by mechanical means and the free tab orend of the tape is grasp-ed by the other hand and pulled or jerked fromthe paper in such a way that the tape is pulled back over itself. Whenit is desired to obtain both a quantitative and qualitative estimate ofthe size of the coating, the tape may be pulled back from the paper bymechanical means which will be described in more detail below. Duringthis removal of the tape from the paper it is essential for consistentresults that the tape pulled back along a line close to the ofithe stockfor itself.

paper and substantially parallel to it. In other words, the tape shouldseparate from the paper at a very acute angle to the surface ofthepaper, say less than 30. The tape is then examined. The presence onthe tape of no paper stock and only a small amount of coating indicatesa hard sized coating and a strong stock. The presence on the tape of aconsiderable amount of coating and no stock indicates a soft sizedcoating and a relatively strong stock. The presence of paper stockusually indicates strong cohesion of the coating for itself and/or arelatively weak stock. Occasionally the paper stock, although notactually pulled off with the tape, will be raised in places formingripples. This rippling of the paper stock indicates that the adhesion ofthe coating to the stock is almost as great as the cohesion The pullingof stock usually ihdicates that the paper is at least sufficiently sizedfor printing purposes.

In another method of carrying out this invention we use a strip of"friction tape about eight to ten inches long and about three quarters ofan inch wide. on the sheet of coated iaper so as to avoid wrinkling, andthen a gear is firmly rolled over the tape once. The gear may be, forexample, of 6 diametral pitch and 4 inches in diameter. One end of thetape is slightly raised from the paper, grasped between the fingers andrapidly pulled or jerked from the paper at a very acute angle to thesurface of the paper, in such a way that the tape is pulled back overitself. The tape will be found to have a number of impressions upon itcoinciding with the contacting positions of the gear teeth. Examinationof each o these This strip is only lightly pressed down.

accuses separate impressions indicates the character of the coating atthese points. This modification of the test is superior to themodification in which the tape is uniformly rolled with a roller,because in the latter case it occasionally happens that the tape willpull paper stock at one portion of the paper and continue to pull paperstock throughout the rest of the pull by virtue of the additional holdthat the adhering paper stock gives. This does not normally occur whenthe tape is in contact with the paperat spaced intervals because thereis no substantial adhesion between the tape and the paper in theintervening spaces.

The preferred method of carrying out this invention consists inseparating the testing agent, for example, ordinary friction tape, fromthe coated paper, after it has been contacted firmly and evenly, by theuse of mechanical means capable of measuring the force or work requiredto effect the separation of the testing agent. In this manner, thecoatings may be tested both qualitatively and quantitatively.

The measurement of the force or the work required to remove the testingagent from the coated paper may be accomplished in a variety of ways.For example, the force required to remove an adhering tape at a uniformvelocity may be measured by any suitable and well known means, forexample, by means of a dynamometer. Or

the tape after being firmly contacted with the.

paper may be attached by means of a loose cord to a falling weight or toa pendulum of known mass which is allowed to pull the tape afterattaining a desired velocity. The distance that the weight or thependulum travels after beginning to pull the tape until it comes to restcan be used as a measure of the adhesion existing between the coatingand the paper stock. In this method of testing, the tape should becontacted over a sufficiently large area so that it is not entirelyremoved from the paper by the pull. In another variation of the test,the tape may be completely removed from the coated paper and theresidual energy of the falling weight or pendulum may be measured in anyappropriate manner. For example, the residual energy may be measured byallowing the weight or pendulum .to fall upon a. spring balance ordynamometer at the moment that the tape is completely removed from thepaper.

In the accompanying drawing we have shown one form of apparatus which issuitable for carrying out the method of this invention in its preferredform. This apparatus is of the pendulum type.

Figure I is a. top veiw and Figure II is a. side elevation of theapparatus in the stable or neutral position.

Figure III shows the apparatus in the position for starting the test.

l is a base equipped with a levelling screw 2. The pendulum 4 is tightlymounted on the sleeve 8' which is capable of revolving about the axis 5which is mounted on the frame 3. A graduated scale 6 is inscribed ormounted on the face of a pendulum in about the position shown. A collar8 carrying the pointer 1 is frictionally fitted to the sleeve 8. Thiscollar has a constant friction just sufiicient to prevent over run ofthe pointer I when the pendulum stops. This constant friction ismaintained by a spring in the head of the pointer. I6 is a stop mountedon the frame directly under the center of gravity of the. pendulum whenthe pendulum is in the neutral position. um rying it as far as the penthe right. The levelling screw 2, is adjusted so that the pointer stopsat Zero on the scale at the highest point reached by l pendulum. linefiat spring pressure is fixed to the base i and serves the doublepurpose of acting as a stop to hold the pendulum in the startingposition. preparatory to starting a test (see Figure ill) and also actsas a brake to prevent the pendulum from oscillating after the test. Ahole ill is drilled in the pendulum directly below its center of gravitywhen the pendulum is in the stable position. Cine end of the cord ii isattached to the pendulum through the hole [8, and the other end to aclip l2. This clip is fastened to the friction tape i3, adhering to thecoated paper being tested M.

In using this apparatus for carrying out the invention a strip offriction tape about eight to ten inches long and about three quarters ofan inch wide is laid evenly upon the paper. The tape is then firmlycontacted to the paper by means of a press. The paper is next removedfrom the press and the end oi the tape furthest from the pendulum isslightly raised from the paper and attached by means of the clip to thecord on the pendulum. During this operation the pendulum is in thestable or neutral position. The coated paper to which the tape isattached and the cord are then aligned with the pendulum so that thepull on the tape will be directly along its length without anyappreciable side pull. The distance of the paper from the pendulumshould be such that the cord is taut when the pendulum is in the neutralposition. The pendulum is then put in the starting position as shown inFigure III with the edge is resting against the edge oi the spring 9.The pointer is adjusted to point di-- rectly downward. The paper is heldfirmly with the hand or by mechanical means while the spring 9 ispressed down, thus releasing the pendulum and permitting it to swingdown by its own weight. As the pendulum passes the neutral point itpulls the tape back over itself from the paper. The resistance due tothe adhesion of the tape to the coated paper retards the pendulum in itsupward course bringing it to a stop. The highest point the pendulumreaches before dropping back is indicated by the pointer on the scale.As the pendulum begins to drop back, the spring Q is again allowed toengage the pendulum, thus acting as a brake and preventing furthermotion of the pendulum.

The test is not limited to having the cord attached at the hole ill. Itmay be attached to any part of the pendulum; for example, we haveobtained good results by attaching the cord at a point near the zero endof the scale.

The method is accurately quantitative only when the testing agent doesnot pull paper stock or ripple. When paper stock is pulled or rippledthe reading is unreliable. The method is adaptable to the condition whenpaper stock is pulled or rippled by contacting the tape to the coatedpaper over regularly spaced areas instead of over a continuous area. Forexample, a thin sheet of paper perforated with a number of holes may beplaced between the coated paper to be tested and the friction tape, andthe tape firmly contacted with the coated paper at the perforated spacesby means of a press. The test is then carried out as described above.Due to the smaller area of contact between the tape and the coated paperthis method gives a lower read-.

A :iot oi the tape is contacted on *i the coated paper. Ob-

ocating is such that the testing agent does not pull paper stock.

In any method cl? carry out this it is usually that jerired or rapidlypulled from the paper. When the tape is jerked or rapidly pulled fromthe paper, it tends to pull coating or coating and stools with it;whereas, if the tape is very slowly removed from the paper, the rubberor other plastic adhesive substance of the tape tends to separate fromthe backing leaving a layer of adhesive substance on the coated paperand failing to give a test.

The tests are sharply differentiated from the sealing was test in anumber of important respects. In the sealing was test the piece of waxmust be lifted from the paper at substantially right angles to thepaper. Slight deviations in the angle of withdrawal cause greatinconsistencies in the results. Slight variations in the angle ofwithdrawal do not affect results in our tests. When the sealing wax ispulled away from the coated paper it breaks away from the wholecontacting area simultaneously. On this account the sealing wax testfails to differentiate between two coated papers which vary onlyslightly in size. In our tests the tape breaks away from the sheetcontinuously substantially along a line instead of from an area. Thismakes it possible to test coatings having a much wider range of sizethan can be obtained with the sealing wax test.

The tests may be conducted with the testing agent laid either with oracross the grain of the paper, and obviously either side of the papermay be tested before or after calendering. The tests can be performedvery quickly and the conditions of pressure, contacting, etc., can bereadily controlled. They are accurate regardless of the waterproofnessof the coating and regardless of the character of the adhesive substanceused in the coating. Furthermore, the tests do not depend, upon thethermo-plastic properties of the adhesive substance. All of these pointsare among the advantages that our tests have over the usual thumb testand sealing wax test.

It is understood that this invention is not limited to the use of anyparticular testing agent such as friction tape nor to any particularmeans of contacting it with the coated paper or or" re moving it fromthe coated paper, nor to any particular means for measuring the force orwork required to remove the testing agent from the coated paper exceptas required by the scope of the appended claims.

In the appended claims by line contact we mean the line of intersectionof the plane of the lOOSe end of the tape with the surface of the paperbeing tested.

We claim:

1. The method of testing the coatings on invention coated papercomprising adhesively contacting a flexible body having a stronglyadhesive surface with a considerable area of the coated paper, suddenlyseparating it from the paper and then examining the surface of saidflexible body.

2. The method of testing the coatings on coated paper comprisingadhesively contacting a flexible body having a strongly adhesive surfacewith considerable area 01 the coated paper, sting the paper by pullingplane of said loose end and the plane of the paper intersect at an angleless than and then examining the suriece oi flexible body.

3. The method of testing the coatings on coated paper comprisingadhesively contacting with the coated paper a strip of flexible material-having a strongly adhesive surface, suddenly separating said strip fromthe paper by pulling it back over itself so that it parts with the paper*substantially along a line contact and then examining the surface ofsaid flexible material.

4. The method of testing the coatings on coated paper comprisingadhesively contacting with the coated paper at spaced intervals, aflexijble strip of tape having a strongly adhesive surface, suddenlyseparating the, strip from the surface of said with the paper a strip ofrubber-impregnated adhesive tape, suddenlyv separating said tape fromthe paper by pulling it back over'itseli' so} that it parts with thepapersubstantially along a line contact and then examining the surfaceof said strip oi tape.

'7. The method oi testing the coatings on coated paper comprisingadhesivelycontacting to a considerable area oi the coated paper a"hexible body having a strongly adhesive surface and measuring the workreguired to ble body from the paper. 8. The method of testing thecoatings on coated paper comprising adhesively contacting to the coatedpaper a strip of adhesive tape and measuring the work required to removethe tape from the paper when the tape is suddenl pulled back overitself. l

9. The method of testing the coatings on coated paper comprisingadhesively "contacting to the coated paper a strip of adhesive tape, at

spaced intervals, suddenly applying a known amount of energy tending topull the tape back over itself, and measuring the distance the tape ispulled from the paper.

10. The method of testing the coatings on coated paper comprisingadhesively cont-acting to the coated paper a strip of adhesive tape,con-- necting the tape to a pendulum, allowing the pendulum after it hasswung through a portion of its arc, to pull the adhesive tape'ba'ck overitself away from the paper, and measuring the work done by the pendulumin partially removing the tape from the paper.

11. The method of testing. the coatings on coated paper comprisingadhesively contacting to the coated paper a strip of adhesive tape at offlexible so that the remove the fieldmeasuring the force required toremove the tape nuances,

spaced intervals, connecting the tape to a pendulumpallowing thependulum after it has swung through a portion 01' its arc, to pull theadhesive tape back over itself away from the paper, and measuring thework done by the pendulum in partially removing the tape irom the paper.

12. The method of testing the coatings on coated paper comprisingadhesively contacting to the coated paper a strip of adhesive tape andmeasuring the force required to remove the tape from the paper.

4 13. The method of testing the coatings on coated paper comprisingadhesively contacting to the coated paper a strip of adhesive tape andmeasuring the energy required to remove the tape from the paper.

14. The method of testing the coatings on coated paper comprisingadhesively contacting to the coated paper a strip of adhesive tape,suddenly applying a known amount 01 energy tending to pull the tape backover itself, and messuring the distance the tape is pulled from thepaper.

- 15. Method of testing coating materials which comprises. adhesivelycontacting thereto 0. flexible body having an adhesive surface, suddenlyapplying. a known amount oi. energy tending to detach said flexible bodyfrom the material being tested along a line contact and measuring thedistance said flexible body is pulled from the material tested.

16. The method 01' testing the coatings on coated paper comprisingadhesively contacting to the coated paper a strip of adhesive tape,connectlngthe tape to a pendulum, allowing the pendulum after it hasswung through a portion of its arc, to partially pull the adhesive tapeback over 'itseli' away from the paper, and measuring the distance thetape is pulled from the paper.

'17. The method of testing the coatings on coated paper comprisingadhesively contacting to the coated paper a strip of adhesive tape andfrom the paper at a uniform velocity.

l8. The method of testing the coatings on coated paper comprisingadhesively contacting to the coated paper a strip of adhesive tape,

I allowing a falling body of known weight after it has attained adesired velocity to partially pull the tape from the paper until saidbody comes to rest and measuring the distance travelled by said bodyafter beginning to pull the tape.

19. The method 01' testing the coatings on coated paper comprisingadhesively contacting tothe coated paper a strip of adhesive tape,

.allowing a falling body of known weight to remove the tape from thepaper and measuring the residual energy of said body.

20.-The method of testing the coatings on I coated paper comprisingadhesively contacting to the coated paper a. strip of adhesive tape,connecting the tape to a swinging body, allowing said body after it hasswung through a predetermined arc to partially pull the tape from thepaper and measuring the work done by the body.

DONALD B. BRADNER. WILLIAM J. MONTGOMERY.

